Device and method for controlling piston position in linear compressor

ABSTRACT

Device and method for controlling a piston position in a linear compressor, having a power source, a triac, and a motor, the device including a current phase detecting part for detecting a current switched at the triac, integrating the current, and generating a first square wave corresponding to the integrated current, a stroke phase detecting part for generating an AC voltage waveform having a fixed frequency and varied amplitude according to a piston reciprocation position following motor operation, and generating a second square wave corresponding to the AC voltage waveform, a zero cross detecting part for detecting a zero crossing of the voltage supplied from the power source, and a controlling part for generating a signal for controlling a piston position according to a phase difference of the first square wave detected at the current phase detecting part and the second square wave detected at the stroke phase detecting part, thereby making an efficiency and a reliability the best by controlling a piston position in a cylinder such that a top clearance becomes a minimum according to a phase difference of a current square wave and stroke square wave.

TECHNICAL FIELD

[0001] The present invention relates to a linear compressor, and moreparticularly, to device and method for controlling a piston position ina linear compressor.

BACKGROUND ART

[0002] A background art device and method for controlling a pistonposition in a linear compressor will be explained with reference to theattached drawings. FIG. 1 illustrates one example of the background artdevice for controlling a piston position in a linear compressor, andFIG. 2 illustrates waveforms of high, regular, and low voltages: fromthe AC-DC voltage transformer in FIG. 1, and FIG. 3 explains adefinition of top clearance.

[0003] Referring to FIG. 1, one example of the background art device forcontrolling a piston position in a linear compressor is provided with apower source 1 for supplying AC 220V, a triac 2 for switching AC 220volt from the power source 1 in response to a control signal, a motor 3operative by AC220V switched thereto through the triac 2 forreciprocating a piston, a stroke generator 4 for generating an ACvoltage waveform having a fixed frequency and varied amplitude accordingto a piston reciprocating position, a rectifying circuit 5 forrectifying the AC voltage waveform generated at the stroke generator 4,a filter circuit 6 for filtering the voltage waveform rectified at therectifying circuit 5 into a DC voltage waveform, an AC-to-DC voltagetransformer 7 for transforming the DC voltage waveform filtered at thefiltering circuit 6 into a corresponding DC voltage, a zero crossdetecting circuit 8 for detecting a zero crossing of AC 220V suppliedfrom the power source 1, a microcomputer 9 for converting the DC voltagefrom the AC-to-DC voltage transformer 7 into a length of pistonreciprocation corresponding to the DC voltage, comparing the length ofthe piston reciprocation to a preset value, and providing a controlsignal according to a result of the comparison, and a phase controllingpart 10 for controlling a firing angle to control a stroke in responseto a control signal from the microcomputer 9.

[0004] The operation of the background art device for controlling apiston position in a linear compressor of the present invention will beexplained.

[0005] When the phase controlling part 10 provides a triggering signalfor a firing angle at an initial drive of the linear compressor, thetriac 2 switches AC220V from the power source 1 to the motor 3, so thatthe motor 3 reciprocates the piston in a cylinder. In this instance, thestroke generator 4 generates an AC voltage waveform having a fixedfrequency: and varied amplitude according to a piston reciprocationposition. And, the rectifier circuit 5 rectifies the AC voltage waveformgenerated at the stroke generator 4, and the filter circuit 6 filtersthe voltage waveform rectified at the rectifying circuit 5 into a DCvoltage waveform. Then, the AC-to-DC voltage transformer 7 transformsthe DC voltage waveform filtered at the filtering circuit 6 into a DCvoltage corresponding to the DC voltage waveform. And, the zero crossingdetection circuit 8 detects a zero crossing of the AC220V from the powersource 1, and provides a signal of a zero crossing detection result.According to this, the microcomputer 9 converts the DC voltage from theAC-to-DC voltage transformer 7 into a length of piston reciprocation,compares to a preset value, and provides a control signal according to aresult of the comparison. That is, the microcomputer 9 converts the DCvoltage from the AC-to-DC voltage transformer 7 into a length of pistonreciprocation corresponding to the DC voltage, compares to a presetlength for a regular stroke voltage under a regular pressure, and, asshown in FIG. 2, as a result of the comparison, if the DC voltage fromthe AC-to-DC voltage transformer 7 is a stroke voltage at a highpressure or a low pressure, provides a control signal for altering thestroke voltage into a stroke voltage at a regular pressure. Then, thephase controller 10 provides a signal for controlling a firing angle tocontrol the stroke in response to the control signal from themicrocomputer 9. That is, the phase controller 10 provides a controlsignal for reducing a firing angle according to a control signal foraltering a high pressure stroke voltage from the microcomputer 9 into aregular pressure stroke voltage, or a control signal for increasing afiring angle according to a control signal for altering a low pressurestroke voltage from the microcomputer 9 into a regular pressure strokevoltage. According to this, the triac 2, triggered by the control signalfrom the phase controller 10, controls a voltage phase of the AC220Vfrom the power source 1, and the motor 3 reciprocates the piston in thecylinder according to a phase controlled at the triac 2. That is, thetriac 2 controls the voltage phase of the AC220V from the power source 1according to a control signal for reducing the firing angle from thephase controller 10, to reduce a current to the motor 3, such that themotor 3 in turn reduces the piston reciprocation length in the cylindershorter, or the triac 2 controls the voltage phase of the AC220V fromthe power source 1 according to a control signal for increasing thefiring angle from the phase controller 10, to increase a current to themotor 3, such that the motor 3 in turn increases the pistonreciprocation length in the cylinder shorter. Thus, by repeating theforegoing process, the microcomputer 9 converts the DC voltage from theAC-to-DC voltage transformer caused by the piston reciprocation in thecylinder into a piston stroke length corresponding to the DC voltage,for controlling a piston position.

[0006] However, the background art device and method for controlling apiston position in a linear compressor has the following problems.

[0007] First, the system is complicate with the rectifying circuit, thefiltering circuit, the AC-to-DC voltage transformer, and there is adifference between an actual position and a fedback position because ofmuch error at a stroke-feedback device, and the error is related to anerror at the circuits inclusive of the errors at the motor and themechanical components, no matter how precisely the system is fabricated,occurrence of collision between the piston and the valves/deteriorationof an efficiency/increase of noise caused by error are not avoidable.

[0008] Second, the system has a poor load estimation capability suchthat, as shown in FIG. 3, load variation at a top clearance portion cannot be estimated, that causes the controlling of the system verydifficult, and prediction of environmental variation(temperaturevariation) and non-regular characteristics in a set state(gas leakage,cycle blocking) is difficult.

DISCLOSURE OF INVENTION

[0009] Accordingly, the present invention is directed to device andmethod for controlling a piston position in a linear compressor thatsubstantially obviates one or more of the problems due to limitationsand disadvantages of the related art.

[0010] An object of the present invention is to provide device andmethod for controlling a piston position in a linear compressor, inwhich a piston position in a cylinder is controlled for minimizing a topclearance.

[0011] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0012] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, thedevice for controlling a piston position in a linear compressor, havinga power source, a triac, and a motor, includes a current phase detectingpart for detecting a current switched at the triac, integrating thecurrent, and generating a first square wave corresponding to theintegrated current, a stroke phase detecting part for generating an ACvoltage waveform having a fixed frequency and varied amplitude accordingto a piston reciprocation position following motor operation, andgenerating a second square wave corresponding to the AC voltagewaveform, a zero cross detecting part for detecting a zero crossing ofthe voltage supplied from the power source, and a controlling part forgenerating a signal for controlling a piston position according to aphase difference of the first square wave detected at the current phasedetecting part and the second square wave detected at the stroke phasedetecting part.

[0013] The current phase detecting part includes a current detectingpart for detecting a current switched at the triac, an integrating partfor integrating the current detected at the current detecting part, anda first square wave generating part for generating the first square wavecorresponding to the current integrated at the integrating part.

[0014] The stroke phase detecting part includes a stroke generating partfor generating the AC voltage waveform having a fixed frequency andvaried amplitude according to a piston reciprocation position, and asecond square wave generating part for generating the second square wavecorresponding to the AC voltage waveform generated at the strokegenerating part.

[0015] The controlling part detects a piston position at which the topclearance becomes a minimum according to a phase difference of the firstand the second square waves and provides a signal for controlling thepiston position at which the top clearance becomes the minimum.

[0016] The device for controlling a piston position in a linearcompressor further includes a rectifying part for rectifying the voltagewaveform of the stroke detected at the phase detecting part, and anAC-to-DC converting part for converting the rectified voltage waveforminto a DC waveform.

[0017] In another aspect of the present invention, there is provided amethod for controlling a piston position in a linear compressor having apower source, a triac, and a motor, including the steps of (1)generating a first square wave corresponding to a current of a voltageswitched at the triac, (2) generating a second square wave correspondingto a stroke occurred as the motor is operated by the voltage, and (3)controlling a piston position by controlling a phase of voltage switchedat the triac according to a phase difference of the first square waveand the second square wave.

[0018] The step (3) is the step for providing a control signal forcontrolling a piston position such that a top clearance becomes aminimum according to a phase difference of the first and second squarewaves.

[0019] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciples of the invention:

[0021] In the drawings:

[0022]FIG. 1 illustrates one example of a background art device forcontrolling a piston position in a linear compressor;

[0023]FIG. 2 illustrates waveforms of high, regular, and low voltagesfrom the AC-DC voltage transformer in FIG. 1;

[0024]FIG. 3 explains a definition of top clearance;

[0025]FIG. 4 illustrates a device for controlling a piston position in alinear compressor in accordance with a first preferred embodiment of thepresent invention;

[0026]FIG. 5 illustrates a device for controlling a piston position in alinear compressor in accordance with a second preferred embodiment ofthe present invention;

[0027]FIG. 6 illustrates waveforms at different components of FIGS. 4and 5;

[0028]FIG. 7 illustrates a phase difference between a current phase anda stroke phase;

[0029]FIG. 8 illustrates shifted paths of a current phase and a strokephase following pressure changes; and,

[0030]FIG. 9 illustrates a difference between a current phase and astroke phase at a pressure.

BEST MODE FOR CARRYING OUT THE INVENTION

[0031] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings. FIG. 4 illustrates a device for controlling apiston position in a linear compressor in accordance with a firstpreferred embodiment of the present invention.

[0032] Referring to FIG. 4, the device for controlling a piston positionin a linear compressor in accordance with a first preferred embodimentof the present invention includes a power source 10 for supplying AC220V, a triac 20 for switching AC 220 volt from the power source 10 inresponse to a control signal, a current phase detecting part 30 fordetecting the current switched through the triac 20, integrating thecurrent, and generating a first square wave corresponding to theintegrated current, a motor 30 operative on the AC220V switched theretothrough the triac 20 for reciprocating a piston in a cylinder, a strokephase detecting part 50 for generating an AC voltage waveform having afixed frequency and varied amplitude according to a piston reciprocationposition and generating a second square wave corresponding to the ACvoltage waveform, a zero cross detecting circuit 60 for detecting a zerocrossing of the AC 220V supplied from the power source 10, a controllingpart 70 for generating a signal for controlling a piston positionaccording to a phase difference of the first square wave provided fromthe current phase detecting part 30 and the second square wave providedfrom the stroke phase detecting part 50, and a phase controlling part 80for controlling a firing angle to control a stroke in response to acontrol signal from the controlling part 70. The current phase detectingpart 30 includes a current detecting part 31 for detecting a currentswitched through the triac 20, an integrating part 32 for integratingthe current detected at the current detecting part 31, and a firstsquare wave generating part 33 for generating the first square wavecorresponding to the current integrated at the integrating part 32. Thestroke phase detecting part 50 includes a stroke generating part 51 forgenerating the AC voltage waveform having a fixed frequency and variedamplitude according to a piston reciprocation position, and a secondsquare wave generating part 52 for generating the second square wavecorresponding to the AC voltage waveform generated at the strokegenerating part 51.

[0033]FIG. 5 illustrates a device for controlling a piston position in alinear compressor in accordance with a second preferred embodiment ofthe present invention, which includes a converting part 90,additionally. The converting part 90 includes a rectifying part 91 forrectifying the AC voltage waveform generated at the stroke generatingpart 51, and an AC-to-DC converting part 92 for converting the ACvoltage waveform rectified at the rectifying part 91 in a DC voltagewaveform corresponding to the AC voltage waveform.

[0034]FIG. 6 illustrates waveforms at different components of FIGS. 4and 5, FIG. 7 illustrates a phase difference between a current phase anda stroke phase, FIG. 8 illustrates shifted paths of a current phase anda stroke phase following pressure changes, and FIG. 9 illustrates adifference between a current phase and a stroke phase at a pressure.What is drawn in the foregoing drawing does not limit the presentinvention. A method for controlling a piston position in a linearcompressor in accordance with a preferred embodiment of the presentinvention will be explained, with reference to the attached drawings.

[0035] Referring to FIG. 4, at an initial operation of the linearcompressor, when the phase controlling part 80 provides a triggeringsignal for a firing angle as shown in FIG. 6C, the triac 20 switches anAC220V as shown in FIG. 6A supplied thereto. Then, the current phasedetecting part 30 detects, integrates a current switched through thetriac 20, and generates a first square wave corresponding to theintegrated current. That is, the current detecting part 31 of thecurrent phase detecting part 30 detects a current as shown in FIG. 6Bswitched through the triac 20. Then, the integrating part 32 integratesthe current detected at the current detecting part 31 as shown in FIG.6D. According to this, the first square wave generating part 33generates the first square wave corresponding to the current integratedat the integrating part 32 as shown in FIG. 6E. On the other hand, themotor 30 is driven by the power switched at the triac 20, to reciprocatethe piston in the cylinder. In this instance, the stroke phase detectingpart 50 generates an AC voltage waveform having a fixed frequency andvaried amplitude according to a piston reciprocation position, and,then, the second square wave corresponding to the AC voltage waveform.That is, as shown in FIG. 6F, the stroke generating part 51 of thestroke phase detecting part 50 generates the AC voltage waveform havinga fixed frequency and varied amplitude according to a pistonreciprocation position. Then, as shown in FIG. 6Q the second square wavegenerating part generates the second square wave corresponding to the ACvoltage waveform generated at the stroke generating part 51. And, thezero cross detecting part 60 detects a zero crossing of the AC220Vsupplied from the power source 10. Then, the controlling part 70generates a signal for controlling a piston position according to aphase difference of the first square wave detected at the current phasedetecting part 30 and the second square wave generated at the strokephase detecting part 50. That is, as shown in FIG. 7A, the controllingpart 70 provides the signal for controlling a piston position as shownin FIGS. 8 and 9 according to a phase difference of the first squarewave detected at the current phase detecting part 30 as shown in FIG. 7Aand the second square wave generated at the stroke phase detecting part50 as shown in FIG. 7B. According to this, the phase controlling part 80controls the firing angle for controlling a stroke in response to thecontrol signal from the controlling part 70. Then, the triac 20 switchesthe voltage supplied from the power source 10 according to the firingangle from the phase controlling part 80. And, as the foregoing stepsare repeated, the controlling part 70 detects a piston position at whichthe top clearance becomes a minimum, and provides a signal forcontrolling the piston position at which the top clearance becomes theminimum.

[0036] And, as shown in FIG. 5, the converting part 90 may be added tothe system in FIG. 3. The converting part 90 includes the rectifyingpart 91 and the AC-to-DC converting part 92, wherein the rectifying part91 rectifies the AC voltage waveform generated at the stroke generatingpart 51, and the AC-to-DC converting part 92 converts the AC voltagewaveform rectified at the rectifying part 91 into a DC voltage waveformcorresponding to the AC voltage waveform. Then, the controlling part 70controls operation according to the DC voltage waveform converted at theAC-to-DC converting part 92, and conducts a process identical to theprocess shown in FIG. 4.

INDUSTRIAL APPLICABILITY

[0037] As has been explained, the device and method for controlling apiston position in a linear compressor has advantages in that anefficiency and a reliability are made the best by controlling a pistonposition in a cylinder such that a top clearance becomes a minimumaccording to a phase difference of a current square wave and strokesquare wave.

[0038] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the device and method forcontrolling a piston position in a linear compressor of the presentinvention without departing from the spirit or scope of the invention.Thus, it is intended that the present invention cover the modificationsand variations of this invention provided they come within the scope ofthe appended claims and their equivalents.

What is claimed is:
 1. A device for controlling a piston position in a linear compressor, having a power source, a triac, and a motor, comprising: a current phase detecting part for detecting a current switched at the triac, integrating the current, and generating a first square wave corresponding to the integrated current; a stroke phase detecting part for generating an AC voltage waveform having a fixed frequency and varied amplitude according to a piston reciprocation position following motor operation, and generating a second square wave corresponding to the AC voltage waveform; a zero cross detecting part for detecting a zero crossing of the voltage supplied from the power source; and, a controlling part for generating a signal for controlling a piston position according to a phase difference of the first square wave detected at the current phase detecting part and the second square wave detected at the stroke phase detecting part.
 2. A device as claimed in claim 1, wherein the current phase detecting part includes; a current detecting part for detecting a current switched at the triac, an integrating part for integrating the current detected at the current detecting part, and a first square wave generating part for generating the first square wave corresponding to the current integrated at the integrating part.
 3. A device as claimed in claim 1, wherein the stroke phase detecting part includes; a stroke generating part for generating the AC voltage waveform having a fixed frequency and varied amplitude according to a piston reciprocation position, and a second square wave generating part for generating the second square wave corresponding to the AC voltage waveform generated at the stroke generating part.
 4. A device as claimed in claim 1, wherein the controlling part detects a piston position at which the top clearance becomes a minimum according to a phase difference of the first and the second square waves and provides a signal for controlling the piston position at which the top clearance becomes the minimum.
 5. A device as claimed in claim 1, further comprising a phase controlling part for controlling a firing angle for controlling a stroke in response to a control signal from the controlling part and providing to the triac.
 6. A device as claimed in claim 5, wherein the triac switches a voltage supplied from a power source according to the firing angle from the phase controlling part.
 7. A device for controlling a piston position in a linear compressor, having a power source, a triac, and a motor, comprising: a current phase detecting part for detecting a current switched at the triac, integrating the current, and generating a first square wave corresponding to the integrated current; a stroke phase detecting part for generating an AC voltage waveform having a fixed frequency and varied amplitude according to a piston reciprocation position following motor operation, and generating a second square wave corresponding to the AC voltage waveform; a zero cross detecting part for detecting a zero crossing of the voltage supplied from the power source; a converting part for rectifying a voltage waveform of a stroke detected at the stroke phase detecting part, and converting the voltage waveform into a DC waveform; a controlling part for generating a signal for controlling a piston position according to a phase difference of the first square wave detected at the current phase detecting part and the second square wave detected at the stroke phase detecting part, and controlling operation according to the DC waveform converted at the converting part.
 8. A device as claimed in claim 7, wherein the converting part includes; a rectifying part for rectifying the voltage waveform of the stroke detected at the phase detecting part, and an AC-to-DC converting part for converting the rectified voltage waveform into a DC waveform.
 9. A device as claimed in claim 7, further comprising a phase controlling part for controlling a firing angle for controlling a stroke in response to a control signal from the controlling part and providing to the triac.
 10. A device as claimed in claim 9, wherein the triac switches a voltage supplied from a power source according to the firing angle from the phase controlling part.
 11. A method for controlling a piston position in a linear compressor having a power source, a triac, and a motor, the method comprising the steps of: (1) generating a first square wave corresponding to a current of a voltage switched at the triac; (2) generating a second square wave corresponding to a stroke occurred as the motor is operated by the voltage; and, (3) controlling a piston position by controlling a phase of voltage switched at the triac according to a phase difference of the first square wave and the second square wave.
 12. A method as claimed in claim 11, wherein the step (1) includes the steps of; detecting a current switched at the triac, and integrating the current to generate a square wave corresponding to the integrated current.
 13. A method as claimed in claim 11, wherein the step (2) includes the steps of; generating an AC voltage waveform having a fixed frequency and varied amplitude according to a piston reciprocation position, and generating a square wave corresponding to the generated AC voltage waveform.
 14. A method as claimed in claim 11, wherein the step (3) is the step for providing a control signal for controlling a piston position such that a top clearance becomes a minimum according to a phase difference of the first and second square waves. 